The present invention relates to hydraulic impedance mechanisms useful in tools for use in oil and gas wells. More particularly, the invention relates to fluid dump mechanisms for bypassing a hydraulic impedance element for providing a sudden release of hydraulically controlled movement between two members of a jar or like apparatus in an oil well.
During certain operations, such as testing or drilling oil wells, a tubular string is lowered into the borehole of an oil well. Many times, the lower end of the tubular string becomes stuck thus preventing removal of the tubular string from the well bore.
Jars of various types have been developed to impart jarring blows to the tubular string when the tubular string is lifted from the surface. These jarring blows may be imparted to the stuck string over a long period of time such that continuous blow may eventually unstick the tubular string so it may be removed.
The jar is typically operated by pulling on the tubular string from the surface. The jar typically includes two tubular sections which are telescoped one within the other. The pulling on the string from the surface causes the two tubular sections to move relative to one another initially at a controlled rate. This controlled rate allows the tubular string to stretch during the pulling operation. At a predetermined point, the controlled movement of the two tubular sections of the jar is released such that the jar may suddenly be released to move to a fully extended position. When the jar is thus fully extended, a hammer on one tubular section of the jar strikes an anvil on the other section to impart a sharp jarring blow to the tubular string.
The apparatus is then returned to its initial position by lowering the tubular string from the surface. The jarring cycle is then repeated by once again pulling from the surface.
In some apparatus, a sudden release of a controlled movement of the tubular string is used to indicate at the surface the operation of some downhole tool. Such a tool is disclosed in U.S. Pat. No. Re. 29,471 to Giroux.
In a hydraulically controlled apparatus, the initial rate of movement between the two tubular sections is typically controlled by a hydraulic impedance mechanism. At some predetermined point, a bypass means is provided to bypass hydraulic fluid flow around the impedance mechanism such that the two tubular sections may move freely to impart the desired blow or give the desired surface indication.
The apparatus of the present invention includes an outer tubular housing and an inner tubular mandrel arranged for telescopic movement with respect to each other. An oil filled chamber is located between the outer housing and the inner mandrel with a flow regulating piston on the inner mandrel dividing the oil filled chamber.
A flow regulating means such as a Lee Visco Jet is provided through the flow regulating piston such that the inner mandrel moves with respect to the outer housing at a controlled rate.
In the illustrative embodiment, a dump valve in the inner mandrel is disclosed which is designed to open after a predetermined amount of movement of the inner mandrel. Upon the opening of the dump valve, hydraulic fluid is freely dumped from one side of the control piston to the other side such that the mandrel may freely slide with relation to the outer housing to deliver a jarring blow of a hammer on the inner mandrel upon an anvil provided on the outer housing.
An opening means for opening the dump valve is disclosed which is releasably attached to the outer housing. The opening means is designed to remain attached to the outer housing until the dump valve means is open, and then to be released from the outer housing and to travel with the inner sliding mandrel holding the dump valve means open until the mentioned jarring blow is struck.
The opening means is moved by the inner sliding mandrel back to its original position during a recocking operation in which the inner mandrel and the outer housing is moved back to the fully extended position.
A bypass means is disclosed in the piston means which serves to bypass the flow control device during the recocking operation.